Control system



May 9, 1944- L. CUNNINGHAM ETAL 2,348,206

' CONTROL SYSTEM Filed May 1 1940 2 Sheets-Sheet-l JNVENTORS LamaLfiunumgham Hams: E.MEZL'JHE Z75] m @TTORNEY.

May 1944- L. L. CUNNINGHAM ETAL 2,348,206

CONTROL SYSTEM Filed May 1, 1940 2 Sheets-Sheet 2 IVENTORS Lewis LEunmngam Humar EMaZmnE 27y W ATTORNEY.

Patented May 9, 1944 CONTROL SYSTEM Lewis L. Cunningham, Glendale,021111., and

Homer'E. Malone, Milwaukee, Wis.,

Perfex Corporation, ration of Wisconsin assignors to Milwaukee, Wis., acorpo- Applicatlon May 1, 1940, Serial No. 332,674

27 Claims.

This invention relates in general to control systems and moreparticularly to heating control systems employing an automaticallyoperated mechanical stoker.

The simplest kind of heating system utilizing a mechanical stoker isthat in which the driving mechanism, such as an electric motor, isoperated by a thermostat which is situated to sense the temperature ofthe space to be controlled. In such a system the thermostat serves tocause operation of the stoker when the temperature 01' the space isbelow a certain predetermined temperature and to cause operation of thestoker to cease if the temperature of the space is above the desiredpredetermined temperature.

During severe weather when the heating system must operate a highpercentage of the time, such a rudimentary system is satisfactory.However, certain difliculties are encountered if this basic system isused without auxiliary control means during mild weather when the stokeris called upon to operate a relatively small per-' centage of the time.Under the latter class of operation the stand-by or "off periods of thestoker are so long in comparison to the operating or on periods that thefire burns itself out between successive on periods.

The customary method of alleviating this trouble is to provide anelectrically operated motor and gear traintiming mechanism whichintermittently operates the stoker for regular on" periods at regularoiP periods. In other words, the stoker is automatically operated for ashort length of time, for example three minutes, whether heat isrequired or not, and then allowed to stand by if no heat is required inthe system for an oii" period of predetermined length, for example sixtyminutes, after which time another automatic on period is initiated. Inthis way fire is maintained in the stoker under all conditions and it isnot necessary to frequently rekindle the fire in mild weather.

The primary object of this invention is to provide a heating systemincorporating a new and improved means for preventing extinguishment ofa stoker fire.

A further object of the invention is to provide a new and improved timerfor a stoker system which does not incorporate high speed andconsequently quickly wearing parts or gear trains.

A further object is to provide a thermal operated timer which isreliable in operation and economical to build.

A further object is to provide a thermal operated timer whose timingfunctions are substantially free from variations due to ambienttemperature fluctuations.

A further object of the invention is to provide new and improved meansfor operating a stoker in response to automatic timer operations and inresponse to the control action of a space thermostat.

A further object is to provide a thermal operated timer which willoperate a stoker for predetermined on periods at regular predeterminedofi periods.

A further object is to provide a thermal operated timer havingadjustable means for regulating the duration of "on" and off periods inwhich the means are so related that the adjustment of one is ineffectiveon the adjustment of the other.

With the system outlined above, the stoker may be automatically operatedby the timer just subsequent to an operation in response to a call forheat by the room thermostat in the space to be heated. If this conditionexists the stoker willrun for a length of time equal to the "on periodof the timer after the stoker has been running a relatively long time inresponse to the room thermostat. Such an automatic operation at thistime is not required to prevent the fire from becoming extinguished, andtherefore serves only to causevover-shooting" of the temperature in thespace being heated.

Certain devices have been incorporated in heating systems of the kinddescribed to prevent such successive operations of the stoker. Thesedevices are commonly referred to as skip cycle" devices and in at leastone form of device the timing mechanism is so arranged that after astoker operation from the room thermostat a full timer "on" period mustelapse before a timer on period may be initiated.

A further object of the invention is to provide means for interposingdelay between operation of a stoker in response to room thermostataction and operation in response to an automatic timer operation.

Other objects and advantages reside in certain novel features ofconstruction, arrangement, op-

eration and combination of the parts and circuits which will beherein'after more fully described in the specification, and particularlypointed out in the appended claims, and of which the preferredembodiments are illustrated in the accompanying drawings.

In the drawings:

Fig. 1 is a plan view showing a timing device of the invention.

Fig. 2 is an elevation in partial cross-section taken along the line2--2 of Fig. 1, but shows the arrangement of the parts at a differenttime during the operation of the timer.

Fig. 3 shows the relation of some of the parts of Fig. l at a certaintime during the operation cycle of the timer.

Fig. 4 shows the operation of some of the parts of Fig. 1 at anothertime during the cycle of operation of the timer.

Fig. 5 shows the relation of the parts of Fig. 1 at a third time duringthe cycle of operation of the timer.

Fig. 6 shows the relation of other of the parts of Fig. 1 at a fourthtime during the cycle of operation of the timer.

Fig. '7 is an isometric view of the control mech-.

anism shown in Fig. 1 modified somewhat for the sake of clarity.

Fig. 8 is a wiring diagram of the component parts of a heating systemembodying the invention.

Fig. 9 is a simplified schematic of the shown in Fig. 8.

Fig. 10 is a modification of the system shown in Fig. 8.

While the invention is susceptible of various modifications andalternative constructions, the drawings shown and the description hereinillustrate the preferred embodiments. It is to be understood, however,that there is no intention to limit the invention to the specific formsdisclosed, but rather to cover all modifications and alternativeconstructions falling within the spirit and scope of the invention.

Generally stated, the invention contemplates the incorporation of athermally operated timer in a stoker fired heating systefn so as toprevent extinguishment of the fire. In the exemplary forms illustratedin the drawings, the invention is embodied in a stoker-fired burnersystem having a stoker timer wherein an electro-thermal actuator isoperable to slowly actuate a switchcontrolling member back and forth tocontrol its own energization in such a manner as to sustain theoscillatory motion, and in this oscillation the switch-controllingmember is operable to control the energization of the stoker in aprescribed manner. The electro-thermal actuator of the timer is arrangedto impart motion to a switch arm in a particular manner in order to bestutilize the time-motion characteristics circuit of the actuator inmeasuring the desired on" and off periods of the stoker.

Two alternative embodiments of the stokerfired burner control system ofthe present invention are illustrated in Figs. 8 and 10 of the drawingsand each of these two burner control tation of a shaft l2. Theresistance I6 is supported upon a suitable means such as the insulatedbobbin l1 and is insulated from the surrounding structure by insulatorsi8 and I9. Means having relatively high thermal inertia is associatedwith the spirally-shaped bimetallic element II and the heatingresistance l6 such as the cast housing 2|. The heater resistance I6 issecured in relatively intimate contact with the housing 2| by means ofclamping it between the metallic ring i3 and the housing 2|. Screws 22passing freely through the metallic ring I3 and screwed into the housing2| serve to provide the necessary clamping force .to secure the heaterIS in correct position. I

Means are provided for confining the heat produced by the heaterresistance Hi to a zone in the immediate vicinity of the spirally-shapedactuator H such as the housing cover plate 23 together with the coverinsulating washer 24. Spacing members 25 and 26 serve to secure thehousing cover plate 23 to the housing 2| by passing through the coverplate 23 and threading into the housing 2|. The spacers 25 and 26additionally provide means for spacing the housing assembly from, butsecuring it to, the insulated panel 21. The shaft I2 is journaled nearthe junction point of the spirally-shaped actuator. II by means of anaperture 28 in the cover plate 23. The other end of the shaft I2 isjournaled in an aperture in a hanger 29 supported in cantilever fashionto the panel 21 by means An oscilof screws 3| and a two-holed nut 32.lating control member such as the switch arm 33 is freely pivoted to theshaft |2 by means of turned up ears 34 and 35. An oscillating actuatorfor the switch arm 33 is additionally freely pivoted to the shaft l2,and as herein shown this systems embodies a stoker timer, theconstructional and operational features of which are illustrated indetail in Figs. 1 to '7.

As shown in Figs. 1 and 2 of the drawings, the timer comprises a thermalactuator such as the spirally-shaped bimetal actuator II which has oneend securely fastened as by spot-welding to a condition transmittingmember such as the shaft l2. The .other end of the spirallyshapedactuator ii is secured to a relatively stationary support such as themetallic ring H by means of a pin l4 passing through an aperture IS inthe spirally-shaped actuator H and driven into a suitable opening in themetallic ring |3. Motivating means for the actuator such as the heaterresistance I6 is placed in the vicinity of the actuator for heating thesame to cause 1'0- oscillating actuator comprises a first driver memberA formed in the general shape of a U having driver sides 36 and 31 and abase 38. A portion of the driver side member 31 is turned down at rightangles to the remainder of the side so as to form a projecting driverlug 39. The driver lug 39 is arranged to protrude through an armate slot40 in the panel 21. The driver member A is motivated by the actuator Ithrough a strain release means which as herein shown comprises an arm 4|having one and engaging the lug 39 and secured at the other of its endsto a hub 42 which in turnis fixed to the shaft l2 by means of screws 43.A helical spring 44 is wrapped around the hub 42. One end of the springis secured to the screw 43, while the other end is arranged to bearagainst the lug 39 so as to bias lug 39 against arm 4|. A projection 45integral with the hub 42 is provided to space the driver side 31 fromthe arm 4|. The projection 45 passes loosely through a suitable aperturein the panel 21.

Suitable lost motion engaging means is provided between the driver A andthe switch arm 33 whereby the switch arm 33 is oscillated back and forthby the driver. This lost motion engaging means comprises a firstmeansfor engaging and motivating the switch arm 33 in a counter clockwisedirection and a second means for engaging and motivating the switch arm33 in a clockwise direction. The first means is shown as a driver stopscrew 46 secured to the driver member by threading through a driver ear41 bent down at right angles to the plane of the driver side 36 andadapted to engage the switch arm. The second means is shown as an on"period adjusting cam 49 pivotally supported on the driver side 35 bymeans of pivot pin 49 passing fully through the cam 48 and riveted tothe driver side 36. A friction washer 5| is provided between the cam andthe driver side to prevent the cam 48 from rotating from the position atwhich it is .set except by manual manipulation.

Means such as the biasing tension spring 52 are provided to bias theswitch arm 33 toward the on period adjustment cam 48 in a counterclockwise direction relative to the driver A for reasons which -will bepointed out hereinafter. One end of the tension spring 52 is connectedto the switch arm 33 by means of a projection 53 therefrom. The otherend of the spring 52 is connected to the driver A as by attaching to thedriver ear 4! by passing through an aperture therein.

Suitable stops are provided for the switch arm 33 so as to limit itsoscillating motion. These are shown as a counter clockwise stop contactscrew 54 and a clockwise stop contact screw 55. The contact screws 54and 55 are mounted on the panel 21 in any suitable way as by means ofsupports 56 and 51. A pair of resilient blades 58 and 59 are suitablysecured to the switch arm and carry contact buttons 6| and 82 for thepurpose of accomplishing certain switching functions in conjunction withthe contact screws 54 and 55. It is preferable to insulate the resilientblades 58 and 59 from the switch arm 33. This may be done by a pair ofinsulating strips 63 lying on each side of switch arm33 as shown inFigs. 1 and 2. Figs. 3, 4, 5 and 6 show the blades as being directlyconnected to the switch arm merely to simplify the illustrations.

Suitable means are associated with each contact screw 54 and 55 to biasthe switching arm 33 toward that contact screw. Such means are shown asa permanent magnet 84 associated with the contact screw 54 and apermanent magnet 65 aisociated with the contact screw 55. The

permanent magnets 64 and 85, the resilient blades 58 and 59, the tensionspring 52 and the bimetal actuator ll cooperate to render first.

the action of the cooperating contacts 6| and 54, and 62 and 55 snapacting to insure good switch action, and second. to render the motion.of the switch arm 33 snap acting in a particular manner to accomplish aprescribed control function as will be more fully explained hereinafter.

As may be seen from the description thus far, when the bimetal actuatorH is subjected to a change in temperature condition by energization orde-energization of the heater IS, the driver A is moved backward andforward, and the motivating effort of the bimetal actuator is applied tothe driver through the strain release members 4|,42andth driver lug 39.The bimetal actuator serves as the actuating or driving member and thedriver A serves as the driven member or load. The driver A loads theactuator to the extent of the load upon it. This load normally, inaddition to the friction load of the pivoting journals, consists of theload encountered in actuating the switch arm 33 back and forth betweenthe contact screw stops 54 and 55. This may be termed the real or usefulload. In addition to this real load, means are provided to in roduceartificial load in order to change the condit on.

of the actuator required to result in movement of the driver to aprescribed position and hence to change the time required for thisfunction as will be hereinafter described. Means for introducing suchartificial load are shown as the cantilever spring 66 suitably securedto the driver base 38 as by means of rivets 61 and its asso= ciateadjustable abutment shown as the support 68 adiustably secured to thepanel 21 by adjusting screw 69 and stop screw 1| threaded through saidsupport 68.

For reasons which will be more fully described hereinafter, a secondoscillating actuator such as a second driver 72 is associated with thefirst driver A and is adapted to engage the switch arm 33 at the tip ofan upward extension 13 at the outer extremity of the switch arm 33. Ears14 integral with the econd driver are turned over to serve as journalbearings for a pivot pin I5 which is riveted to the hanger 29. Anactuating pin 16 is fixed in the ears 74 at a point somewhat remote fromthe pivotal axis of the pivot pin 15. This actuating pin 16 extends fromthe bottom of the second driver 12 into an arcuate cam slot 1! in thefirst driver A, the arrangement being such that when the first driver Aoscillates back and forth the sides of the arcuate slot 11 engage theactuating pin 16 and cause the second driver 72 to oscillate back andforth. The pivot axis of the second driver 72 is remote with respect tothe pivot axis of the first driver A and the actuating pin 16 of thesecond driver 12 is so situated that the rate of oscillatory movement ofthe second driver 12 is much greater than that of the first driver A?The function of this second driver 12 will be more fully explainedherein' after, but to digress a moment it may be said that the seconddriver 12 serves to take control over the switch arm 33 independent ofthe controlling action of the on period cam 48 of the first driver Awhen the switch arm 33 is being returned to its most clockwise position,in order that the off period timing will be substantially constantregardless of the setting of the on period cam.

In the stoker control system of Fig. 8 the timer is showndiagrammatically with its switch arm 33 in two of its positions. Thesolid lines designate the extreme clockwise position where the switcharm contact blade 59 is in contact with the contact stop and the dottedposition'designates the extreme counterclockwise position where thecontact blade 58 is in contact with the contact stop 54. Conductors 78and 19 designate conductors connected to the electric service main. 8|is a limit control" such as is ordinarily used in automatic heatingsystems. It may be responsive to either pressure temperature or to anyother suitable physical condition. Fig. 3 shows this limit control 8| tobe in full command over the entire system and to cause absoluteshut-down of the system in the event that conditions are in excess ofthe value for which the limit control 8| 'is set. Fig. 10 shows thelimit control 8| in a different branch of the heating system circuit inorder to effect a different mode of operation as will be explainedhereinafter.

Referring to Fig. 8. conductor 82 is connected to conductor '18 throughthe limit control 8| and serves as a feeder for several branch circuits.

- One of these circuits partially extends from the conductor 82 throughthe switch arm 33 by means of the conductor 83 connecting the twotogether. If the switch arm is in the clockwise position as shown.circuit extends through the clockwise contact stop 55, through theheater is, to the other service conductor 19. If the switch arm 33 is inthe counterclockwise position, the circuit extends through thecounterclockwise contact stop 54, a ballast resistor 84. a conductor 35.an electro mechanical device such as a relay coil connected to theconductor 85 at the junction of the ballast resistor 84 and the relaycoil 86. A secondary of the transformer is arranged to be shunted bymeans of a physical condition responsive means such as the spacethermostat 88 located in a space to be controlled. Another circuitextends from the feeder conductor 82 through the relay switch contacts88, through conductor 9| to the motor 32 of the stoker to be controlledand thence to the other service conductor 13. Through this circuit poweris supplied to the stoker motor 92 whenever the relay contacts 89 andthe limit control 8| are closed.

The stoker control system illustrated in Fig. 10 is basically identicalwith Fig. 8 but the circuit position of the ballast resistor 84 ischanged and the space thermostat 88 is arranged to directly control therelay circuit rather'than to indirectly do so through an impedancetransferring device such as the transformer 81 shown in Fig. 8.

Operation Referring now particularly to the mode of operation of thetimer, assume that all parts are at room temperature. Under theseconditions thee bimetal actuator ll, because of prior operation, willhave rotated the shaft I2 to its extreme clockwise position and thestrain release arm 4| will have moved away from the driver lug 39limiting the stress on both the actuator H and the driver A to thatproduced by the rotating effort of the helical spring 44. Above thepanel 21 the parts will assume the positions shown in Fig. 1 with boththe switch arm 33 and the drive A in their extreme clockwise positionsand with the contact button 62 engaging the contact stop screw 55.

When the device is first connected to the electrical service main, thelimit control 8| being closed, current will flow from the conductor I8,through the limit control 8|, the conductor 82, the conductor 83, theswitch arm 33 (actually resilient contact blade 58), the contact button82, the contact stop screw 55, the heater Hi to the other serviceconductor I8. This current flow energizes and causes the heater toincrease its temperature. This in turn causes the bimetal actuator II toheat and effects a counterclockwise rotary motion of the shaft l2.Inasmuch as considerable mass is associated with the heater IS in viewof the massive housing 2|, the temperature conditions within the bimetalactuator enclosure increase very slowly. After some lapse of time thestrain release arm 4| engages the driver lug 39 and causes the driver Ato slowly rotate about the axis of shaft I! in a counterclockisedirection. As soon as the driver A starts to rotate, the on" periodadjusting cam 48 moves away from the switch arm 33, since while thetension spring 52 biases the switch arm 33 in a counterclockwisedirection with respect to the driver A, the magnetic effort of thepermanent magnet 85 tends to bias the switch arm 33 in a clockwisedirection and the latter being of predominating magnitude restrains theswitch arm 33 in a position against contact stop 55. After some lengthof time the driver A rotates sufficiently to cause engagement ofthe'driver stop screw 48 with the switch arm 33. When this position isreached, the driver A will cease further motion for an interval of timewhile the bimetal actuator continues to heat and stores up energy. Aftersome further length of time suflicient effort will have been built up inthe actuator II in a counterclockwise direction against the switch arm33 to overcome the clockwise restraining efiort ofthe magnet on theswitch arm 33. Immediately thereafter the switch arm 33 will snap in acounterclockwise direction from its position against the contact stopscrew 55 to a position against the stop screw 54. That is, it willtraverse the gap between the contact screws 85 and 54 in one full snap.

Fig. 3 shows the position of the parts immediately preceding thesnapping operation described above while Fig. 4 shows the arrangement ofthe parts just subsequent to the snap. Inasmuch as the effort deflectioncharacteristics of the magnet 65 and the biasing spring 52 arediametrically opposite and correctly proportioned, the switch arm 33will snap away from the magnet 85 under the influence of the bias spring52, as soon as the arm 33 is moved slightly away from its stop positionproximate to the magnet 65. At the time the switch arm 33 snaps intdengagement with contact 54, the driver A has rotated to a position inwhich a gap is present between the switch arm and cam 48. Thus initialclockwise motion of driver A merely closes the gap without actuating theswitch arm.

As soon as the switch arm 33 moves away from the contact stop screw 55as described above, the circuit to the heater IE is broken and theheater begins to cool, causing the clockwise rotation of the driver A.As the driver moves in a clockwise direction in response to the coolingof the bimetal actuator II, this gap diminishes and finally completelycloses. Immediately following the closure of this gap the driver A stopsits rotation while the bimetal actuator builds up sumcient effort toovercome the magnetic attraction the permanent magnet 64 has for theswitch arm 33. When sufficient effort has been built up to overcome thisforce, the switch arm 33 snaps away from the magnet 64, the snap in thiscase being derived from the resiliency of the actuator cooperating withthe peculiar attraction properties of a permanent magnet.

Referring to Fig. 8, it will be noted that while switch arm 33 is in itsmost countercl'ockwise position against the stop screw 54 a circuit isestablished extending from service conductor 18, through limit control8|, conductor 82, conductor 83, switch arm 33 (actually resilient blade58), contact stop screw 54, ballast resistor 84, conductor 85, relaycoil 86, to the other service conductor I9. While this circuit is closedthe relay coil 88 is energized and its contacts 89 are engaged. Therelay contacts 89 being engaged, close acircuit for the stoker motor 32extending from service conductor 18 through limit control 8|, conductor82, relay contacts 89, conductor 8|, stoker motor 92, to the otherservic conductor 19. Thus it will be seen that while switch arm 33 is inits position against the contact stop screw 54 the stoker will operate,and when it is not in such a position the stoker will not operate(except in response to the space thermostat 88 which will be more fullydescribed hereinafter).

The length of time that the switch arm 33 is in this counterclockwise orburner control position determines therefore the length of on period,and this in turn is determined by the length of time it takes for the onperiod cam 48 to move from its most counterclockwise position to aposition against the switch arm 33 with sufilcient effort to disengageswitch arm 33 from contact with contact stop screw 54.

It will be seen that when the driver and the switch arm 33 are both intheir most counterclockwise positions, the gap between the engagingportion oi the on period cam 48 and the switch operating arm 33 is a,certain amount. This amount of gap may be increased by rotating the onperiod cam 48 in a clockwise direction about its pivot pin 49. Byadjusting the size of this gap by such rotation the on period is changedinasmuch as the deflection required, and

V hence the length of time required, for the driver A to rotate asuflicient amount to engage the cam 48 with the switch arm 33, ischanged. In other words, the on period is determined substantially vbythe length of time required for the driver A to move from its mostcounterclockwise position to a position where the cam 48 engages theswitch arm 33, and as the amount of deflection required to accomplishthis is varied so the length of on" period is varied, the time requiredfor a deflection being a direct function of the amount of thedeflection.

It will be noted that when the switch arm 33 snaps away from the magnet64 in a clockwise direction it snaps but a short distance away from themagnet 64, because when travelling in this direction there is only theresiliency of the bimetal actuator II to move the switch arm 33 awayfrom the magnet 64. This should not be confused with the magnitude ofthe snap in the counterclockwise direction where the switch arm 33 snapsall the way across in view of additional resilient action of the biasingspring 52.

Now assume for the moment that the second driver 12 were removed. Ifthis were true, the on period cam after disengaging the switch arm 33from the contact stop 54 would continue to rotate the switch arm 33,remaining in engagement with it until the switch arm 33 approached theimmediate vicinity of the magnet 65; the

- switch arm 33 and the driver A rotating together as a unitarystructure. Under these conditions when the switch arm 33 came within theimmediate vicinity of the magnet 65 the magnetic attraction inopposition to the resilient effort of the tension spring 52 would causethe switch arm 33 to snap in a clockwise direction to engage the contactstop screw -55 and consequently close the circuit extending through theheater l6. Upon the heater l6 again being energized, the bimetalactuator would again deflect in a counterclockwise direction causing thedriver A to again start the cycle described above.

It will be noted, however, that when the bimetal actuator H is energizedafter one cycle has been traversed the temperature thereof is not roomtemperature but is somewhat elevated above it. After one cycle has beentraversed the strain release arm 4| does not leave the driver lug 39.The strain release is only provided to take care of the transientcondition to which the device is subjected when first installed or aftera power failure or limit control operation when the limit control 8| isin the circuit position indicated in Fig. 8.

After the control has gone through the first 7 cycle the bimetalactuator H operates within two temperature limits, the lower limit beingthe temperature requiredto cause the switch arm 33 to just close thecontacts at contact stop 55 when returning to this position after an excursion away from it; and the upper limit being the temperature requiredto bring the stop screw 46 in engagement with the switch arm 33 withsufficient effort to cause the switch arm 33 to snap away from themagnet 65. If the off period of the timer be defined as the length oftime expiring between two automatic on periods, it will be seen thatthis off period corresponds to the length of time required for theswitch arm 33 to move in a clockwise direction away from the magnet 64toward the magnet 65 and then again to return to the magnet 64. In termsof temperature of the bimetal actuator H the off period will initiate ata temperature almost, but not quite, the maximum temperature of thebimetal, will continue on while the bimetal temperature decreases andthen again increases, and will terminate when the bimetal temperaturereaches its maximum. The interval between the maximum tempera-- ture ofthe bimetal and the point described as almost maximum above, being theon" period.

In terms of the driver motion the off period corresponds approximatelyto the length of time required for the driver A to move from its ex-=treme counter clockwise position to its extreme clockwise position andreturn. This in turn. is

governed by the rate of cooling the bimetal actuator ll.

As was set forth above, the bimetal actuator H can only heat while theswitch arm 33 is in engagement with the contact stop 55. Consequently,if means were provided to lengthen the time for the driver A to returnthe switch arm 33 to its clockwise position, then the length of timeexpiring during the Off period would also and heating of be increased.The cantilever spring serves as the means to this end. So long as thecantilever spring fifi'oscillates back and forth with the driver Awithout encountering any obstruction which will set up a restrainingforce, the driver A oscillates as described above. Under theseconditions the load on the bimetal actuator ii is the load transmitted:through the driver and is made up of the various friction loads of thepivots plus that required to oscillate the switch arm 33. This may besaid to be the active load. Now, artificial load is placed upon theactuator if an obstruction such as the stop screw H is placed in thepath of the cantilever spring 36 so that the spring 63 must strike thisabutment somewhere near the terminal portion of the clockwise motion ofthe driver A. With this artificial load on the actuator II, in orderthat the driver member A may be rotated to a position suflicient toclose the contacts at contact stop 55, bimetal actuator H must be at asomewhat lower temperature than it would be if the artificial load wereabsent. This necessarily results since the bimetal actuator II is aresilient member and in order to produce any motion it must internallystress itself, and consequently the greater the load upon the actuatorthe greater it must stress itself in order to produce a givendeflection. It will be seen that as the stop screw H is moved in acounter clockwise direction so that the spring 66 engages it at anearlier point in its counterclockwise direction of travel, the bimetalactuator it must stress itself to a greater extent in order to returnthe switch arm 33 to its circuit closing position in contact with thecontact stop 55. It follows in consequence of such adjustment of stopII, that the bimetalactuator H must cool to a lower temperature toproduce this greater stress with which to effect closure of the abovecontacts and that further the length of time required for such coolingwill necessarily lengthen. Also, since the temperature of the bimetal atthe time of closing of the contacts at contact stop 55 is lower when thestop screw ll engages the cantilever spring 66, than it would be if thestop screw H would not engage the spring 65, the length of time requiredfor the driver A to move from the position shown in Fig. 1 to theposition shown in Fig. 3 will be increased. This increase will be equalto the length of time required for the bimetal temperature to increasefrom its now lower temperature to the temperature it would have had atthe time of closing of the contacts at contact stop 55, in the absenceof engagement of the cantilever spring 65 with the stop screw H. Inother words, by moving the support 68 so as to cause engagement of thestop II with the cantilever spring 65 at an earlier or later time thelower temperature limit the bimetal actuator ll must reach during acomplete cycle of the timer is decreased or increased respectively. Bydecreasing this lower limit time is added to the oiT' period during aportion of both the cooling and the heating cycles of the bimetalactuator ll. Suitable reference marks are engraved on the panel 21opposite the support 68 in order that the stop 1| may be set to effectany desirable length of off period within'the range of the instrument.

The reason for the second driver member 12 will now be explained. In thedescription above the function of the arm 12 was completely eliminatedin order to more clearly set forth the basic idea upon which the timingdevice op erated. For reasons now to be advanced it will be seen that itis desirable that some means be introduced in order to render the off"period timing substantially constant as the on" period timing isadjusted by means of manual manipulation of the on period cam 48. As wasstated above, when the on period cam 48 is rotated in a clockwisedirection the gap between the engaging edge of the on period cam 48 andthe switch arm 33 is increased (when the parts are in the position shownin Fig. 4.) This is done in order that the driver A be made to rotate agreater number of degrees in a clockwise direction from its extremecounterclockwise position before the switch arm 33 is disengaged fromcontact stop 54. While this accomplishes the desirable function ofincreasing the on" period timing by changing the relative position ofthe driver A with respect to the switch arm 33 at that time in thecycle, it also changes the relation between the driver A and the switcharm 33 at every other position of the parts. Consequently if the switcharm 33 were to be returned to its position against the magnet 55 solelyby the action or the on period cam 48, the ex treme clockwise positionof the driver member A would be materially changed. This change wouldvary with the setting of the on period cam.

If no additional structure were used, as the on period cam 48 is rotatedclockwise the temperature of the bimetal actuator H to effect closure oithe contacts at contact stop 55 would decrease and consequently the offperiod would be altered in much the same way as it is by introducingartificial loading. In order to prevent this undesirable result thepresent invention provides means to insure that the temperature of thebimetal actuator H at the time of closure of the contacts at the contactstop 55 will be substantially constant for any given setting of the offperiod adjuster independent of any setting of the on period adjuster.

As was set out hereinbefore, the second driver 12 is operated directlyby the movements of the driver A but is adapted to oscillate back andforth at a-higher rate of movement than is the driver A. In order torender the "01? period timing constant, it is apparent that it isimmaterial what the characteristics of the motion of the switch arm 33are during its clockwise movement from magnet 64 to 65, but that it ismaterial that the switch arm 33 be ready to snap to its contact closingposition against the contact screw 55 when the driver A is in a certainposition in space. This position corresponds to a definite temperatureof the bimetal actuator II and is almost, but not quite, the extremeclockwise position the driver A would assume were the on periodadjustment cam 48 set at the minimum on period setting. It is thefunction of the second driver 12 to have the switch arm 33 in a positionready to snap against contact stop 55 when the dri er A reaches thisdefined position, and to accomplish this irrespective of the position ofthe on period cam 48. If the second driver 12 is so arranged that itjust engages the switch arm 33 at this position of the driver A when theon period cam is set at its minimum position, the desired controlfunction set out above will follow.

With this arrangement of the parts, it might be said that the seconddriver 12 becomes the controlling member in returning the switch arm 33to its contact closing position against the contact stop 55. If the on"period adjustment cam 48 is rotated so as to produce a longer on periodtiming the position of the driver A at the time of closure of thecontacts at contact 55 does not change. This is true since irrespectiveof the position of the cam 48 the second driver 12 will always be in aposition to close the contacts at the contact stop 55 when the driver Areaches a position corresponding to the correct closure point of thesecontacts. As the on period cam 48 is adjusted the second driver "I2 willpick up" or engage the switch arm 33 at an earlier or later time in itsreturn movement toward magnet 65, but switch arm 33 will always be in aposition ready to snap toward magnet 55 when driver A reaches itsappointed position in space.

i As the on period adjustment cam is regulated for increasingly greaterlengths of on period timing the second driver 12 picks up or takes overthe return motion of the switch arm 33 at successively earlier times inthe return travel of the switch arm 33 toward the magnet 65. Where thesecond driver 12 picks up the switch arm 33 is of course immaterial, theonly material factor being that the switch arm 33 be in circuit-closingposition with respect to contact stop 55 when. the driver A rotates tocertain position in space as defined above.

As far as this return function of the second driver is concerned, it isimmaterial as to what the actual rate of motion is so long as it is notless than the rate of motion of the driver A. But it will be seen uponfurther examination of the structure that the second driver 72 mustoscillate at a greater rate than that of the driver A for anotherreason, namely, that there be no obstruction in the path of the switcharm 33 when it is ready and in a position to snap from magnet 65 tomagnet 84 under the action of the stop screw 46.

The relation of the second driver 12 with respect to the other membersof the structure may perhaps be best seen by reference to Fig. 6 whichshows the second driver 12 in position just subsequent to taking thecontrolling function, over the switch arm 33, away from the on periodcam 48 and just prior to the snap of the switch arm 33 to its circuitclosing position against contact stop screw 55. It will be seen that thesecond driver 12 in this instance takes over the controlling function solate in the return cycle of the switcharm 33 because the on periodadjustment cam is in almost its minimum on? period adjustment position.If the "on period adjustment cam were in a position to render longer onperiods the second driver would assume its control action earlier in thereturn cycle.

It is to be understood that after the bimetal actuator II has gonethrough one complete cycle it operates between two temperature limitswhich are substantially greater than ambient temperature. While thelower limit temperature varies depending upon the off period adjustment,both limits always remain substantially above ambient temperature. As aresult varia tions in room temperature of reasonable magnitude do notappreciably affect the time required for the bimetal actuator II and itsassociate housing to change from the lower limits to the high and viceversa. That the above should be true follows from the fact that arelatively high percentage change of temperature at the ambienttemperature becomes only a relatively small percentage change at anelevated temperature.

While the relay86 of the stoker control system of Fig. 8 is energizedfor regular on'** periods at regular off periods in response to theaction of the timer as described above, it may also be energized at anytime in response to the action of the space thermostat 88 irrespectiveof the control action of the timer. When the space thermostat contactsclose, the secondary or the transformer 81 is short circuited. Thisreflects or transfers a low impedance into the primary circuit andeffectively electrically places the relay coil 86 across the conductors82 and 19 in series with the internal impedance of the transformer 81 asit appears from the high voltage winding, energizing the relay andcausing the stoker motor 92 to operate the mechanical stoker.

With the circuit shown in the Fig, 8, the thermostat 88 and the timer,control the stoker motor 92 independently of each other (with theexception that if either device is in a position so as to operate themotor 92 the other of the devices cannot interrupt this operation). Itis obvious with this class of operation that the timer may automaticallycause the stoker to operate in any conceivable time sequence subsequentto an operation by the space thermostat 88 so that it is possible that atimer initiated on period may occur directly after or a short time afterthe room thermostat 88 has caused the stoker to operate. Inasmuch as insome types of heating systems this may produce objecsubstantially,assumes room tionable overshooting, it is desirable to correlate theoperation of the timer and the thermostat to produce a skip-cycle modeof operation.

In the instant device the mode of operation of the timer may be changedto produce the skip-cycle effect by changing the heater lead byconnecting the heater Hi to the conductor 9! rather than to theconductor 19. This change is indicated in Figure 9. With the circuit sorearranged it will be seen that the heater l6 cannot be energized unlessthe relay contacts 89 are in the open position and that then theenergization is through the stoker motor 92. With this arrangement whenthe space thermostat 88 causes the relay coil 86 to close contacts 89the heater l6 cannot be energized by closure of the contacts at contactstop 55. As the result, when the room thermostat 88 calls for heat theheater I6, and consequently the bimetal actuator l I, will commence tocool or will continue. to cool, de pending upon the location of theswitch arm 33. If, for example, the switch arm 33 were just on the vergeof snapping from its position against the magnet 65' to its positionagainst the magnet 64 so as to initiate a timer on period and if at-thisinstant the room thermostat closed its contact so as to operate thestoker, the arm 33 would not snap because the slight amount ofadditional heat required to produce the last small increment of eifortin the bimetal actuator would not be forthcoming, as a consequence ofdeenergization of the heater l3. Now all during the operation of thestoker inresponse to the space thermostats call for heat the bimetalactuator and its associate housing will cool. The length of time thiscooling operation continues depends upon the length of time that theburner operates. As soon as the thermostat 88 opens its contacts theheater again energizes and the length of time required for the driver Ato again be in a position to actuate the switch arm 33 from its positionagainst magnet 65 will be approximately equal to the length of time thatthe room thermostat was operating the stoker. That the delay time andthe period of operation caused by the thermostat should be approximatelyequal is due to the fact that the rate of heating and cooling of thebimetal actuator and its associate housing is substantially the same. Ofcourse, if the periodof operation of the stoker by means of the roomthermostat is of such duration that the bimetal actuator and itsassociate housing temperature, the time delay introduced after athermostat operation will be that length of time required to heatthe'bimetal actuator and its housing from room temperature to thetemperature required to effect actuation of the switch arm 33 in acounterclockwise direction as described in the opening paragraphs ofthis discussion relative to the operation of the timer. It is alsoobvious that if the operation of the stoker by the room thermostatexceeds the length of time mentioned immediately above, the delay timeafter such operation will be constant.

It will be noted that with the wiring illustrated in Figures 8 and 9 thelimit control B! is in series with the entire control system.Consequently,

desirable or necessary, the limit control 8| may be wired in series withonly the room thermostat as indicated in Fig. 10. In such case, thelimit control will permit operation of the stoker regardless of boilertemperature or pressure.

It should be noted that the transfer impedance device or transformer 81is used merely to provide for operation of the relay 8G in response to alow voltage room thermostat. If there is no advantage in using a lowvoltage thermostat the transformer 81 may be dispensed with and thethermostat connected directly across the circuit gap left by theomission of such transformer. In the case of Fig. 8 the ballast resistor84 is made to have substantially the same impedance as the internalimpedance of the transformer 81 so that the voltage drop across therelay 85 and the consequent heating of the relay will be substantiallythe same regardless of whether the room thermostat 88 or the switch arm33 is effecting operation of the relay 86. If the room thermostat isused as a high voltage device as shown in Fig. the ballast resistor 84would have no utility in the position shown in Fig. 8. For this reasonthe change shown in Fig. 10 is made. If a suitable relay coil were usedin Fig. 10 the ballast resistor 84 might be entirely eliminated. In thecase of Fig. 8, if an ideal transformer 81 having no internal impedancewere available then also the ballast resistor 84 shown there might bedispensed with.

Although it is not essential to the satisfactory operation of thedevice, it should be noted that applicants prefer to arrange the bimetalelement II in such a manner that it is not intimately connected with thehousing 2| or the metallic ring [3. This is done so that the temperatureof the bimetal element ll may be elevated above that of the housing 2|.If the bimetal element II were intimately associated with the metallicring l3 or the housing 21 heat transference from one of the elements tothe other would tend to maintain the bimetal element ll substantially atthe same temperature as that of the metallic ring I3 and housing 2| atall times during the heating cycle. In the instant structure when theheater I 6 is de-energized, after having caused the bimetal element IIto have rotated the driver mechanism in a counterclockwise direction soas to disengage the contact 62 from the contact screw 55, thetemperature of the bimetal element H is elevated above that of thehousing 2|. This is due to the'fact that the heat emanating from the hotwire of the heater l6 traverses the air space between the heater I6 andthe bimetal II and heats the bimetal I l by means of direct radiation.Since the bimetal element H has very little mass, the heat so receivedelevates its temperature to a considerable extent. While the blmetalelement II is heating, the housing member 2| is also heating but sincethe mass of the housing member 2| is very much greater than that of thebimetal element ll, its temperatures rise is relatively slow with theresult that at the termination of the heating period the temperature ofthe bimetal element II is elevated above that of the housing member 2|as before stated. Immodiately upon the deenergization of the heater I6both the housing 2| and the bimetal element ll start to cool. Now, sincethe bimetal element II is at an elevated temperature with respect to thehousing 2| and of low mass, it tends to cool rapidly until it approachesthe temperature of the housing member 2| which is cooling slowly, andfrom that point on the bimetal element H and the housing 2| cooltogether at a relatively slow rate. cooling of the bimetal element IIfor a short period of time until it approaches the temperature of thehousing 2| and then there is a relatively slow cooling effect of boththe bimetal element II and the housing 2| as the housing 2| cools toambient temperature.

It will be understood that this rapid cooling of the bimetal element lloccurs during the time that the on period is being measured and causesthe driver A therefore to move a considerable amount during this time.This arrangement has the advantage of providing appreciable deflectionof the driver A with respect to the switch arm member 33 during the on"period and is conducive to a more accurate measurement of the on periodand enables the device to be calibrated with ease.

What is claimed is:

1. In a mechanism of the class described for intermittently operating aheating system for regular on" periods at regular off periods, a memberoscillating between first and second positions at regular intervals, anactuator for the oscillating member, means for energizing the actuatorwhen said oscillating member is at one of said positions, means foroperating said heating system for the duration of said on period whensaid oscillator is at the other of said positions, and means forimparting snap action to the oscillating member in the traverse of themember from the first position to the second position and retardedaction in the traverse of the member from the second position to thefirst position.

2. In a mechanism of the class described for intermittently operating aheating system for regular on" periods at regular off periods, a freelypivoted member oscillating between first and second fixed stops, saidfixed stops including means for exerting restraining effort upon saidoscillating member whereby a predetermined amount of force is requiredto move said oscillating member away from said stops, an actuator formotivating the oscillating member, a lost motion connection between saidoscillating member and said actuator, including first and secondengaging means to effect motion of the oscillating member, one of saidengaging means arranged to impart motion to the oscillating member inone direction, and the other of said engaging means arranged to impartmotion to the oscillating member in the opposite direction, means forbiasing the oscillating member toward one of said engaging means, one ofsaid engaging means arranged to initiate motion of the oscillatingmember away from said first stop, said biasing means arranged tocontinue said motion and cause engagement of the oscillating member withsaid second stop, the other of said engaging means arranged to engagesaid oscillating member and initiate return motion thereof away fromsaid second stop, a second actuator cooperating with the first actuator,said second actuator arranged to continue said return motion and causeengagement of the oscillating member with said first stop, slow actingdriving means for actuating said first and second actuators, controlmeans including the oscillating member for controlling said drivingmeans and effective when the oscillating member engages its first stopto cause movement of the first actuator to shift the oscillating memberfrom its first stop toward its second stop, said control means causingsaid driving means to actuate the first and second actuators in theoppo- In efiect there is a relatively rapid V 2,348,208 site directionwhen the oscillating member isa'way .and control means effective fromsaid "first stop, 1 when the, oscillating member engages itssecond stopto cause operationwoi the heatingisystem- 3. In a burner timer'mechanismfor intermitburner t0. provide alternate -and return movement mountedoperable when saidactuator acts on said control member through itslostmotion in the other direction to impart av snap action movement tosaid control" member from said timer control in said first direction toI her to its timer control position, and timer means er operatingposition, means operable upon'said 4 control member when said actuatoracts on said control member through its lost motion in the otherdirection to impart a snap action to said control position, after inmeans'operable-by said actuator theres return movement in said otherdirecand rendered effective when the control member is in its timercontrol position to cause movement member away fromsaid burner operatingv or the-control member away from said timer com I trolposition;

4. In a burner timer mechanism for intermittently operatinga burner toprovide alternate on and off periods each of predetermined duration, thecombination of I a'control member mounted for oscillation througha-limited range, between aburn'ercontrol position and a timer controlposition, an oscillating actuator having. a lost motion actuatingconnection with said contimer control position to its burner controlposition, means operable upon said control member when said actuatoractson said control member through its lost'motion in the otherdirectionto impart a snap action to said control member away from said burnercontrol position, and means .op-

erable thereafter during return movement of said.

said other direction to'impart a furactuator in ther force tosaidcontrol member to move the same tosaid timer controlposition.

5. Inaburner timer mechanism for intermittently operating aburner'toprovide alternate "on" E d. ofiir duration, the combinationof a controlrnember mounted for oscillation throu'gh limited range between aburnercontrol position and a timer control position, an oscillating actuatorhaving a lost motion actuating connection with said control memberoperable in a firstdirection of move.- ment to impart a first actuatingforceto said control member to move the same from said burner controlposition toward said timer con trol position and thereafter to impart asecond actuating force to said control member to move periods eachof.predetermined.

'first direction to impart positionto its burner control position, meansoperable upon said control member when said actuator imparts said firstactuating force to said control member through its lost motion in said asnap action to said control member away from said burner controlposition, said actuator thereafter being operable by the application ofsaid second actuating force move said control memacting to'osc'illatesaid actuating member and gover'ned-bysaid' control-member in its timercontrol position. a I

6. ma system ofthe class described for operatac tuating'said relay, atiming mechanism for automatically operating said relay independent ofthe action-of saidtransfor'mer, said timing to said shaft,

and second stops at regular intervals, an actua- I said one stop, meansfor operating said heating the same to said timer control position,means device for the duration of said on period when said oscillatingmember is against the other of said stops, means for adjusting thelength of time said oscillating member is against said latter stop llating member away whereby the 011" means for varying oscillating memberwhereby the oil' be varied.

9. In a mechanism of the class described for intermittently operating aheating system for regular on periods and regular 011" periods, a freelypivoted member oscillating between first and second fixed stops, saidfixed stops including means for exerting restraining effort upon saidoscillating member whereby a predetermined amount of force is requiredto move said oscilirom said stops, a driver for motivating theoscillating member, a lost motion connection between said oscillatingmemperiod may be varied, and the time of oscillation of said her andsaid'driver including first and second engaging means to eflect motionof the oscillating member, one of said engaging means arranged to impartmotion to the oscillating member in one direction, and the other of saiden'- gaging means arranged to impart motion to the oscillating member inthe opposite direction, means for biasing the oscillating member towardone of saidengaging means, one of said engaging means arranged toinitiate motion of binationof, control means responsive to the demandfor heat from the stoker for placing the period may same into and out ofoperation, timing .means comprising a member arranged ior oscillationbetween first and second positions, actuating means for said memberarranged to cause movement of said member from the first position towardsaid second position upon energization thereof and for causing movementof said member from the second position toward the first Vposition upondeenergization thereof, means the oscillating member away from saidfirst stop,

said biasing means arranged to continue said motion and cause engagementoi the oscillating member with said second stop, the other of saidengaging means arranged to engage said oscillating member and initiatereturn motion thereof away from said second step, a second driver Icooperating with thevfirst driver, said second driver arranged ,to'continue said return motion and cause engagement ing member and saidsecond stop cooperatingof the heatingwhile engaged to cause operationsystem for the duration of the on period, means for actuating the driverthrough aprescribed time cycle at predetermined intervals and adjustablemean for regulating the degree the first driver is affected by theactuator Ior varying the period of the prescribed time cycle at whichthe driver is actuated,

10. A control system for an intermittently operating device, thecombination of, control means responsive to the demand for operation ofthe device for placing the same into and out of operation, timing meanscomprising a member arranged for oscillation between first and secondpositions, actuating means for said member arranged to cause movement ofsaid member from the first position toward said second position uponenergization thereof and for causing movement of said member fromthesecond position toward the first position upon deenergizationthereof, means controlled by said member for energizing said actuatingmeans when the member is in its first position for causing movement ofsaid member toward said second position and for deenergizing saidactuating means when the member is in its second position for causingmovement thereof toward its first position, means for placing the deviceinto operation when said member is in its second position and forcausing said device to be out of operation when the member is in itsfirst position, and means normally preventing said timing means fromplacing said device into operation for a substantial period oi! timeafter operation of said device by said control means.

11. A control system for a stokerythe comof the oscillating member withsaid first stop, said oscillating member and time after the controldevice from a first position upon movement of said actuator irom -one ofits positions, and means including a secstatic actuator adapted to movein one direction its second position and for controlled by said memberfor energizing said actuating means when the member is in its firstposition for causing movement of said member toward said second positionand for deenergizing said actuating means when the member is in itssecond position for causing movement thereof toward its first position,means for placing the stoker into operation when the member is incausing the stoker to be out of operation when the member is in itsfirst position, and means for preventing energization of said actuatingmeans by said member when the stoker is operated by said control meansfor normally preventing operation of said stoker by said timing meansuntil a period of stoker is placed out of operation.

12. A timing device comprising, a thermostatic actuator adapted to movein one direction upon rise in temperature and to move in the oppositedirection upon fall in temperature, electric heating means for saidactuator, means controlling said heating means to cause alternateheating and cooling of said actuator, a control device. means includinga first actuating member actuated bysaid actuator and effective to movesaid position to a second ond actuating member actuated'by said actuatorand'eflective to move said control device from tinued movement of theactuator in the same direction.

13. A timing device comprising, a thermoupon rise in temperature and tomove inthe opposite direction upon fall in temperature, electric-heatingmeans for saidactuator, a first control means operated by said 'actuator'upon movement thereof from one of its positions'to an intermediateposition, and a second control means operated by said actuator uponcontinued move ment in the same direction, one of said control meansvarying the efiect of said heating means for cooperating in causingalternate heating and cooling of said actuator.

14. A timing device comprising, a thermostatic actuator adapted to movein one direction upon rise in temperature and to move in the oppositedirection upon fall in temperature, electric heating means for saidactuator, a switch for controlling said electric'heating means, acontrol device, means actuated upon said actuator reaching apredetermined temperature for substantially simultaneously actuatingsaid control device and said switch in a manner causing reversal intemperature of said actuator, said actuator after a predeterminedreversal in temperature thereof causing further actuating 0 said controldevice, and upon continued chang in temperature in the same directionactuating said switch.

15. In a system for operating'a heating devict havingfafburnena source.of power-of'high potential for operating the burner, a relay forcontrolling the burner, saidrelay having a coil'and a switch actuatedthereby for connecting the burner with the source'of power, a firstenergizing circuit for the relay'coil, a thermostatically controlledelectric current controlling means for controlling said energizingcircuit to startj an'd stop the burner in accordance with the. demandfor heat, a second circuit 101 the its other position, and meansincluding second switching means operated with the movable mje'mber'forcontrollingsai'd second circuit-jandar r ranged to cause operationof the burner when the movable member is in said other position,

second position with snap action, and to move slowly toward its firstposition.

18. A timing device comprising, a thermostatic element having electricheating means therefor, means including switching means positioned uponmovement of the thermostatic element due to cooling thereof forenergizing said electric heating means and positioned upon movement ofthe thermostatic element due to heating thereof for deenergizing theelectric heating means, to cause the thermostatic element to oscillatebetween hot and cold positions,"spring means for restraining movement.of the thermostatic element in means including-switching meanspositioned upon J movement of the thermostatic element ,due to 1 6. Inasystemfior operating a heating jdevice havinga burner, means includingafirst circuit adapted when'clofsed to, causeoperation ofthe,

burner and when ope-n to. permit; the burner to i burner'independentlyof said first circuit,- burner control. switching means for opening andclosing said second circuit, slow acting timer means f'adapted whenenergized to. move from a 'first position we second position-and adaptedwhen deenergized' to return tor-the first positiOIL' said timer meanswhen in its second position causing stop, thermostatic electriccurrentcontrolling means. for controllingsaid-Hfirstcircuit to start"and stop the burnerin accordance:withthefdee mand forv heat,means-includinga-second circuit adapted when: closed to cause, operationofj'-thecooling direction for increasing the length of timel'requir'edfor movement of the thermostatic 1 .element-incooling-direction,'andadjusting means for said spring m eans =for varying the speed of.the'timing device.

'19 A timing device comprising, a thermostatic element having electricheating means therefor,

cooling thereof for energizing said electric heat- 'ing-means andpositioned upon movement of the thermostatic element jdue' toheatingthereof for deenerg'izing t eelectric heating means, to causethethe'rmostaticelement to oscillate between hot andcold positions,-spring means acting on said thermostatic element forwvarying the lengthof ,time re'quire'd'formovement oft-he thermostatic element in onedirection, and ad-justing'means for said spring means for varying thespeed of the timing devices a 20. A timing device comprising, athermostatic element having electric-heating -means therefor,

- -means' including switching means positioned upon movement of thethermostaticielement due to coolingthereof for energizing said electricheating means andpositioned upon movement of the thermostatic elementdueto heating thereof for deenergizingthe electric heating means, to causethe thermostatic element to oscillate between hot and cold positions, acontrol device actuated said burner control switching means toclose saidsecond circuittfO op ratethe burner, and means includingtimer-controlswitoh ing mcansactuated by said timer means iorcontrolling the same,

said second-switching 'means being positioned when the timer mean is in,itsfirst position for energizing the timer meansj 17. In a system foroperating a heating device having a burner, means including a firstcircuit 1 adapted when 'closed to, causeoperation of the burner andwhen'open to permit theburner to" "stop,- thermostatic electric currentcontrolling means for controlling said first circuit to start and-stopthe burner in accordance with the de- 7 mandfojr'jheat, means includingasecond circuit adapted when closed to cause operation of theburneriinde'pendently of said first circuit, burner ,controi switchingmeans for opening and closing saidjsecond circuit, slow acting timermeans adapted when energized to move from a first position to a secondposition and adapted when deenergized to return to the first position,said timer means when in its second position causing said burner controlswitching means to close said second circuit to operate the burner,means including timer control switching means actuated by said timermeans foncontrolling the "same, said second switching means beingpositioned when the timer means is in its first-position for energizingthe timer means,a'nd means 'includ- 'ing snapaction means for causingthe timer means to move from its first position to its upon movementofthe- 'thermostatic' element to :and-irom its' hot position, adjustablemeans for retarding movement of the" thermostatic element in coolingdirection, and means for rendering said retarding means ineffectiveuntil after the control device is actuated by cooling movement of thethermostatic element.

21. A timing device comprising, a thermostatic element having electricheating means therefor,

' means including switching means positioned upon movement of thethermostatic element due to cooling thereof for energizing said electricheati-ng means and positioned upon movement of the thermostatic elementdue to heating thereof for deen'ergizing the electric heating means, tocause the thermostatic element to oscillate between hot and coldpositions, a control device actuated upon movement of the thermostaticelement from one of its positions toward the other position, adjustablemeans for applying force to said thermostatic element for varying therate of movement of the same toward said other position, and means forrendering said force applying means ineffective until the control deviceis actuated.

22. A timing device comprising, a thermostatic element having electricheating means therefor, switching means forfintermittently energizingsaid electric heating means in a manner causing saidthermostatic elementalternately to movev in. one direction and then the other, a

control device, lost motion type actuating means from its hot positionfor energizing the electric heating means, this causing heating of thethermostatioactuator for moving the movable element to its hotpositionwherein the electric heating means is deenergized, means including imostatic actuator toward said one position, first adjusting means forvarying primarily, the degree of temperature reversal of the"thermostatic actuator required; to efiect said partialuretum snapaction mechanism constructed and arranged to impart snap action to theentire movement of the movable element from one of said positions to theother of said positions while permitting a timed movement of saidelement in the reverse direction, and adjusting means for varying theamount of lost motion provided by said lost motion type motiontransmitting means.

24. A timing device comprising, a thermostatic actuator having electricheating means therefor, a movable element shiftable between hot and coldpositions, lost motion type motion transmitting means between themovable element and thermostatic actuator, means including a switchpositioned when the movable element is away from its hot position forenergizing the electric heat-' ing means, this causing heating of thethermostatic actuator for moving the movable element to its hot positionwherein the electric heating means is deenergized, means including snapacand arranged to oscillate between two positions,

means including switching means operated by the thermostatic actuatorfor controlling the electric heating means, and being actuatedwhen thethermostatic actuator is in one of its psitions for causing continuedmovement of the actuator to its other position, said switching meansalso being constructed and arranged to reverse ,the temperaturechange'of the thermostatic ac- ,tuator when in its other position so asto cause return movement of the actuator to said one position, a controldevice actuated in one man ner upon the thermostatic actuator reachingsaid other position and actuated in the opposite manner u'pon partialreturn movement of said thermovement Ofjfth thermostatic actuator forthereby determining th length of time the controll device 'ismaintainedactuated in said one manner, and second adjusting means for varyingprimarily the degree of temperature reversal of the thermostaticactuator required to-efiect the remaining'return movement to saidoneposition for varying the time between successive actuations of saidcontrol device.- I

26. A timing device comprising, a thermostatic actuator havingelectricheating means therefor and arranged to oscillate between two positions,means including switching means operated by the thermostatic actuatorfor controlling the electric heating means, and being actuated when thethermostatic actuator is in one of its positions for causing continuedmovement of the actuator to its other position, said switching meansalso being constructedv and arranged to reverse the temperature changeof the thermostatic actuator when in its other position-so as to causereturn movement of the actuator to said one po- 7 sition, a controldevice actuated in one manner upon the thermostatic actuator reachingsaid other positionand actuated in the opposite manner' upon partialreturn movementot said thermostatic actuator towardsaid oneposition, and

adjusting means for varying prirnarily the degree of temperaturereversal of the thermostatic actuator required to effect said. partialreturn movement of the thermostatic actuator for thereby determining thelength of time the control device is maintained actuated in said onemanner.

27. A timing devicecomprisinga thermostatic actuator having electricheatingfmeans therefor and arranged to oscillate betweentwo positions,means including switching meanstope'rated by the thermostatic actuatorfor controlling the electric heating means, and being actuated when thethermostatic actuator is in one 01.-its l; 0sitions for causingcontinued movement lof the actuator to its other positionrsaid switchingmeans also being constructed and arranged to reverse the temperaturechange of the thermostatic actuator when in its other position so as tocause return movement of the actuator to said one position, a controldevice actuated in one manner upon the thermostatic actuator reachingsaid other position and'actuated in the opposite manner upon partialreturn movement of said thermostatic actuator toward said one position,and adjusting means for varying primarily the degree of temperaturereversal of the thermostatic actuator required to effect the remainingreturn movement to said one position for varying the time betweensuccessive actuations of said control device. LEWIS L. CUNNINGHAM. HOMERE. MALONE.

